Steam plant and controller



P 1953 R. L. HARRIS ETAL STEAM PLANT AND CONTROLLER Filed June 26, 19514 Sheets-Sheet 1 PRESSURE INVENTOR5 08597- A. #4205 MP6! Ian/zap Arra/vi) p 1958 R. 1.. HARRIS ETAL 2,853,058

STEAM PLANT AND CONTROLLER Filed June 26, 1951 4 Sheets-Sheet 2INVENTOR5 f/G. Z Pail-Er A. Mae/5 Mara: tar/leap Sept. 23, 1958 4Sheets-Sheet 5 Filed June 26, 1951 INVENTORS 4 08527 A Mme/5 M44605lazy/pa FIG. 3

Sept. 23, 1958 'R. L. HARRIS ETAL 2,853,058

STEAM PLANT AND CONTROLLER I 7 Filed June 26, 1951 4 Sheets-Sheet 4 16.!F/6.5 v F16. 7 4/ 1/ I N V EN TOR5 P0551274 Maw/5 BY Maya/5 [an/Pa?United States Patent O STEAM PLANT AND CONTROLLER Robert L. Harris,Benicia, and Marcus Lothrop, Berkeley,

Calif, assignors, by mesne assignments, to Yuha Consolidated Industries,Inc, San Francisco, Calif., a corporation of Delaware Application June26, 1951, Serial No. 233,614

2 Claims. (Cl. 122-448) The invention relates to means for the automaticcontrol of steam power plants, particularly of the portable variety. Anexample of the general environment in which the invention is effectiveis disclosed in the patent of Harris and Lothrop, 2,596,968, issued May20, 1952v and entitled Steam Power Plant.

A power plant of the type referred to is characterized by the provisionof a steam generator as distinguished from a steam boiler. A boiler isusually considered to be a vessel in which the temperature and pressureof the steam bear a fixed relationship to each other since a large bodyof water is always present. A. steam generator is sometimes referred toas a forced circulation or series tube generator and is characterized bythe fact that the pressure and temperature of the steam do not bear afixed relationship to each other, the steam being somewhat at randomsuperheated or saturated or even wet. Some control devices, particularlyas illustrated in Patent Number 1,898,083 issued to Warren Doble, onFebruary 21, 1933 have been generally effective for providing steam ofthe desired pressure and temperature under normal conditions in mosttypes of operation. Under some unusual and special types of operation,the control is not as satisfactory as might be desired and particularlywhen the portable plant is on a vehicle and is subject to a good deal ofvibration and motion, the control also tends to become erratic.

It is therefore an object of the invention to provide a steam plantcontrol effective under virtually all conditions to provide steam of thedesired temperature and pressure.

Another object of the invention is to provide a controller effective togovern the fire and water input to a steam generator in such a way thatthe resulting steam will very closely approximate the desired pressureand temperature.

A further object of the invention is, to provide a control system whichis effective despite vibration and rough handling.

A still further object of the invention is to provide a control systemof a simple nature readily applicable to virtually any steam generatorwithout requiring special construction of the generator.

Another object of the invention is to provide a control system whichpromptly returns the pressure and tempera.- ture of the steam to the setvalues if a substantial deviation accidentally occurs.

An additional object of the invention is. to provide a steam plantcontroller readily set or adjusted to different values of steam pressureand temperature at different times and effective to sustain such setvalues indefinitely.

A still further object of the invention is in general to improve steamplant controllers.

Other objects, together with the foregoing, are attained in theembodiment of the invention illustrated in the. ac.-

companying drawings and described in the. accompanying description.

In the drawings:

Figure 1 is a schematic diagram of a power plant of the type shown inthe copending Harris et a1. application, above identified, butincorporating the general subject matter of the present steam plantcontroller, various parts being shown according to standard schematicillustration and other parts being shown diagrammatically.

Figure 2 is a front elevation with the cover removed of a control boxforming part of the steam plant controller, certain portions beingbroken away to reduce the size of the figure.

Figure 3 is a side elevation of the structure shown in Figure 2, certainportions being in section and certain portions being broken away.

Figure 4 is a fragmentary view, partially in section on the line 44 ofFigure 2 showing one of the controller elements utilized in the controlbox.

Figure 5 is a schematic view in part and is in part a side elevation ofa controller element in one position.

Figure 6 is a view similar to Figure 5 but showing the controllerelement in an intermediate position.

Figure 7 is a view similar to Figure 5 but showing the controller in adifferent position.

Figure 8 is an isometric view showing a part of the proportionalcontroller, certain parts being broken away to reduce the size of thefigure.

Figure 9 is a cross section similar to Figure 4 of a part of theproportional controller in one position.

Figure 10 is a view similar to Figure 9 but showing a different positionofv the parts.

Figure 11 is a view similar to Figure 9 but showing a still furtherchange in the position of the parts.

Figure 12 is a graph illustrating the general relationship of steamtemperature and pressure established by the steam plant controller inone adjusted position.

The complete arrangement of a steam plant to which the controller isespecially adapted is shown in the men.- tioned copending application.It includes an internal combustion engine 6 as a source of power fordriving the various necessary auxiliaries. The engine has a speedgovernor 7 for maintaining the speed of the engine at set values despitevariations in load upon the engine. The governor is subject, among otherthings, to control by a. solenoid 8 which places the governor in engineidling speed and another solenoid 9 which places the governor at amedium engine speed especially for starting from cold. By means of adrive shaft 11 the engine is connected to revolve a positivedisplacement water pump 12, preferably of the reciprocating plungertype, having an inlet pipe 13 extending from a water reservoir 14. Thepump inlet valve 16 preferably of. the poppet check type is left aloneto operate normally or is held open by a solenoid 17. The pump, althoughalways revolving, can be made ineffective to pump water at all.. Whenthe solenoid 17 is de-energized, the inlet valve is continuously heldopen by a spring and the water then merely surges back and forth in thepump inlet. When the solenoid 17 is energized, the spring is. overcome,the inlet valve operates normally and the pump then is effective to pumpwater through an outlet. pipe 18 into a steam generator 19. This is ofthe series tube or forced circulation; type in which the pressure andtemperature do not necessarily bear any fixed relationship to eachother.

The generator 19 is heated by means of a burner 21 having a forced draftblower 22 driven from the shaft 11. The burner is supplied with fuel oilthrough a nozzle. 23. receiving fuel under pressure from a suitablydriven pump 24 and derived from a reservoir 26. A bypass pipe 27 leadingback to. the reservoir 26 is provided with a valve 28 controlled by avsolenoid 29. The arrangement either bypasses fuel from the pump back tothe reservoir 26 so that the burner 21 is inoperative or closes; thebypass entirely or partially so that appropriate fuel is released fromthe nozzle 23 to burn and supply heat to the generator 19.

The pressure and temperature of the steam issuing from the generatorsteam pipe 30 near a main throttle 31 are utilized as impulses forcontrolling the operation of the generator controller. For that reason,we provide a pressure line 32 connected to the steam pipe 30 andextending to a control box 33 at a suitable location. A thermostat 34 isdisposed alongside the steam pipe 30 to sense the temperature thereofand extends to the control box 33. As especially shown in Figures 2 and3, the control box conveniently includes a base plate 36 apertured tooverlie a thermostat tube 37 enclosing a thermostat rod 38 and extendingfrom the casing of the generator 19. Appropriate jam nuts 39 serve asdetachable fastenings for the base plate 36. The operation of thethermostat is such that the rod 38 moves axially within the tube 37, theposition and extent of relative motion of the rod depending upon thetemperature of the steam in the generator.

The pressure line 32 extends to a mounting block 41 on the base plate 36from which a Bourdon tube 42 projects. The free end 43 of the Bourdontube changes its position in direct accordance with the pressureexisting within the pipe 30. There is thus provided adjacent the baseplate 36 of the control box a movable member 38 indicative of the steamtemperature and a movable member 43 indicative of the steam pressure.Upstanding from the base plate 36 are brackets 44 and 46 serving asjournals for a shaft 47 freely rotatable therein. The shaft 47 is turnedby the thermostat rod 38. A lever 48 secured by a pin to the shaft isurged into contact with the rod 38 by a spring 49, see Figs. 2, 3 e. g.

One of the functions of the control system is to energize the solenoid 9when the temperature is low in order that the auxiliary engine 6 willoperate at its medium speed. The control system is supplied withelectricity from a battery 51 having a ground 52 and a master switch 53in a main conductor 54. An appropriate means completes an electriccircuit between the main conductor 54 and a conductor 56 extending tothe solenoid 8. The main conductor 54 extends through a pressureresponsive switch 57 normally closed at all pressures below apredetermined value and normally connected therefore to a conductor 58leading to a steam-up switch 59.

All of the switches utilized in the control box are substantiallyidentical and are particularly designed so that they are not disturbedby vibration and pitching and lurching of a vehicle on which they mightbe installed, yet they are very closely responsive to small changes inoperating conditions. The switch 59, see Fig. 3 for example, includes abase 61 secured by fasteners 62 to the base plate 36. Extending from thebase 61 is a fulcrum upright 65 on which an armature 63 is pivoted. Thearmature is urged away from an electromagnet 64 by a coil spring 66strung between the overhanging end of the armature and a bracket on theupright 65. A keeper 67 on the electromagnet 64 confines the armature 63to relatively narrow oscillation. A main contact point 68 is located onthe other end of the armature 63 in opposition to a main contact point69 on an upright 71 upstanding from the base 61. The electrical circuitsand connections are more apparent from the wiring diagram appearingpartially in Figures 5, 6 and 7 and in Figure 1 but the effect of theenergization of the electromagnet 64 is to pull the armature 63downwardly to close the contacts 68 and 69 to complete a circuit betweenthe main terminals of the relay.

As shown particularly in Figure 4 illustrating a similar switch in adifferent location, the under auxiliary contact 72 for controlling anauxiliary circuit to the electromagnet 64 is carried on an offset duplexframe 73. The frame has twin legs 74 (see Fig. 2) carried by a pivot pin76 extending between upstanding cars 77 on the armature 63. The motionof the armature is therefore imparted to the offset frame 73. In orderthat the frame may be adjustably positioned with regard to the baseplate 36, it is fabricated with an offset lip 78 carrying an internallythreaded boss 79 through which a threaded adjusting screw 81 isdisposed. The adjusting screw has a noncircular head held by a detent 82and when appropriately rotated, lifts or lowers the frame 73 to raise orlower the under auxiliary contact 72. The under contact 72 and theadjusting screw 81 are at slightly different radii from the pin 76 andthe resulting difference in motion results in a slight lateral action ofthe end of the screw with respect to the plate 36. To permit this slightmotion yet to keep the frame 73 firmly in position at all times, arelatively strong spring 83 is connected to a hook 84 on the plate 61and to a book 86 on the frame 73. By appropriately rotating the screwhead 81, the under contact 72 is positioned as desired within arelatively wide range and once positioned, is firmly so held.

Cooperating with the under auxiliary contact 72 is an upper auxiliarycontact 87 at one end of a bolt 88 (see Figs. 2, 4) passing through andso secured to a contact lever 89 (see Figs. 2, 57). The bolt 88 alsoacts as a fastening for an auxiliary circuit wire 91 extending to theelectromagnet 64. The lever 89 at one end is journalled on the pin 76independently of the frame legs 74 and is urged into contact closingposition by a coil spring 92 (Figs. 2 and 4) at its lower end secured toa hook 93 projecting from the upright 65. A pin 94 spanning a depression96 in the lever 89 engages the spring either in the looped, upper endthereof, as illustrated in Figure 4, or through the convolutions of thespring in the event the spring is stretched above the lever 89 to affordgreater contact pressure.

The end of the contact lever 89 remote from its fulcrum pin 76 lies inthe path of a lever 181 (Figs. 2, 3) extending from a hub 102 held by apin on the shaft 47 and thus moving in response to temperature. Thesetting is such that at all relatively low temperatures the lever 101 isspaced from and is below the lever 89 but upon the attainment of apredeterrnnied temperature, the lever 101 abuts the lever 89 and movesit about its fulcrum 76 to separate the auxiliary contacts 72 and 87.

Shown especially in Figure 5, in the normal condition of the apparatus,the auxiliary contacts are closed, energizing the electromagnet 64,pulling the armature 63 against the urgency of the spring 66 and closingthe main contacts 68 and 69 so that the solenoid 9 (Fig. l) is energizedto move the governor 7 to its medium position and the apparatus operatesat a medium or steamup speed. When the armature 63 is down, the pin 76is likewise pulled down with it, as shown in Figure 5.

As the arm 101 rises with increasing temperature (moves counterclockwise in Figures 3 and 5), it eventually comes into abutment withthe lever end 89 and begins to lift that end of the lever. The liftingaction takes place against the urgency of the spring 92 and is primarilyabout the rod 76 as a fulcrum. The instant that the auxiliary contacts72 and 87 are slightly separated or are so lightly in abutment that thecurrent flow through the electromagnet 64 is small, the electromagnetloses all or most of its attractive force. The spring 66 is then solelyeffective and rocks the armature 63 not only to open the main contacts68 and 69 and so deenergize the solenoid 9 but likewise lifts thefulcrum pin 76. The lever 89 is then supported on the lever 101 and onthe lifted pin 76. This action is shown progressively in Figures 6 and7.

Figure 6 is an instantaneous position in which the auxiliary contactshave broken to deenergize the electromagnet but the electromagnet hasnot yet responded. In Figure 7, not only have the auxiliary contactsbeen opened but the electromagnet has been deenergized and to anexaggerated degree, the armature 63 has lifted under the influence ofthe spring 66. The armature is then supported only at two points;namely, onits fulcrum support 65 and against the stop 67 (Fig. 3).Furthermore, the lever 89 is supported at only two points, one of thembeing on the lever 101 and the other being on the fulcrum 76. The spring92 is then effective to hold the lever against vibration and abnormaldislodgment. The important factor is that a slight separation of theauxiliary contacts not only breaks a circuit atthat point but alsocauses a bodily displacement of the contact lever 89 because of theresulting motion of the fulcrum pin 76.

Assuming that the temperature. now falls, the lever 101 revolves in thereverse direction (moves clockwise in Figures 3 and 5) and begins tolower the outermost end of the lever 89. Under the influence of thespring 92 and the lowering lever, the auxiliary contact 87 finally abutsthe auxiliary contact 72. The position of the lever 101 at which thisreabutment takes place is not the same as the position at which theauxiliary contacts were first broken. Due to the intervening change ofposition of the fulcrum pin 76, the contacts 87 and 72 come together ata lower temperature than the temperature at which they broke. Thisdifference in temperatures is a function of the design of the apparatusand can be established at substantially any interval desired.

As soon as the auxiliary contacts 87 and 72 are again in abutment,current again flows to the electromagnet 64 and the armature. 63 isagain attracted. Since the contacts 37 and 72 are already in abutment(even a very light abutment), the movement of the armature 63 toward theelectromagnet 64 moves the fulcrum pin 76 downwardly under the urgencyof the spring 83 so that the adjusting screw 81 is slightly displacedwith respect to the base 36 but more important, the outboard end of thelever 89 is lifted off the actuating lever 101. Again the contacts 87and 72 are in firm abutment, and the main contacts 68 and 69 are also infirm abutment. The pressure of the spring 83 is effective to hold theauxiliary contacts together while the strengthof the electromagnet iseifective to hold the main contacts 68 and 69 together.

Since the outboard end of the lever 89 is lifted slightly ofi of theactuating lever 101,.the full force of the spring 83 holds the auxiliarycontacts closed and any minor vibration and surging movement of thelever 101 or of the mounting is ineffective to cause the auxiliarycontacts to chatter. Because the contacts close at a position of thelever 101 diiferent from that at which they open, the contacts remainvery firmly pressed together when they are closed, remain completelyapart when they are opened and no chattering or hunting of the systemoccurs.

According to this arrangement therefore, the thermostat is eftective atall temperatures below a predetermined or set temperature as establishedby the position of the regulating screw 81 (Fig. 3) to causeenergization of the solenoid 9 so that the auxiliary engine 6 operatesat a medium speed and drives the pump 12 and the blower 22 at a mediumspeed for steaming up. As soon as a set temperature is reached in thegenerator 19, the thermostat opens the steam-up switch 59, the solenoid9 is deenergized and the governor 7 drops the speed of the engine 6 toan idling value.

A similar arrangement is provided to be effective at a maximum settemperature. The shaft 47 carries an arm 121 elfective to operate thelever 122' of a temperature switch 123 identical with the switch 59. Theswitch 123 is included in a circuit connected to the conductor 58 andextending through a conductor 124 to the solenoid 29 which governs thesupply of fuel to the nozzle 23. When the temperature is low, the switch123 is closed, the solenoid 29 is energized and fuel is not bypassed bythe pump 24 but is sent to the nozzle 23 for burning. When thetemperature rises in the generator 19 to a. set or predetermined valueas established by the adjusting screw of the temperature switch 123, thelever 122 is lifted and by the same-sequence. of operations aspreviously described, the circuit to the solenoid 29 is interrupted, thevalve 28 is opened, the fuel oil bypasses and the burner 21 no longeroperates to supply heat to the generator 19.

To make the pressure responsive mechanism 42 effectice, the terminus 43(Fig. 3) of the responsive device is connected by a link to a lever 126journalled on or freely mounted on the rod 47. The motion of the rod 47and of the lever 126 are not dependent upon each other. The lever 126moves in both directions only in response to the motionof the tube end43. The lever 126 carries a rod 127 underlying a lever 128 forming partof the pressure switch 57 identical with the switches 59 and 123. Underlow pressure conditions, the switch 57, being connected to the mainconductor 54 and being normally closed, is effective to complete acircuit through the conductor 58 thereby permitting any of the connectedinstrumentalities 59, 123, 141 e. g. to be appropriately energized. Whenthe pressure rises to a predetermined value, the end 43 through the link125 lifts the lever 126 and by means of the rod 127 actuates the lever128 to open the circuit thereby shutting down all of the electricallycontrolled apparatus. When the pressure again falls for any reason, theswitch 57 is again closed permitting energization of the circuits.

The control system, as so far described apart from the steam-upmechanism, is effective merely to turn off the supply of heat to thegenerator at a maximum temperature and to interrupt both the supply ofheat and the supply of water at a maximum pressure.

In accordance with the invention, means are provided for controlling thesupply of Water and heat in an additional fashion so that thetemperature and pressure of the steam furnished by the generator notonly have fixed or established maximum values, but likewise have relatedvalues throughout the entire range of pressure and temperature. Asillustrated in Figure 12, there is shown a standard water saturationcurve A indicating the relationship of pressureand temperature in aclosed vessel containing a large mass of water. The curve indicates thatfor each particular steam temperature, there is a corresponding steampressure. The curve is hardly applicable to a series tube generator.Because of the length of the generator tubing and its small diameter andthe directional flow, itis quite possible to have water, wet steam,saturated steam and superheated steam all in the same tube. The steampressure and temperature at the tube outlet do not, therefore, bear anyfixed or necessary relationship to each other.

In accordance with the invention, not only is a pressure of say, fifteenhundred pounds per square inch utilized to interrupt the operation ofthe heat supply and the water supply and not only is a temperature of900 degrees Fahrenheit, for example used to interrupt the supply ofheat, but also a set relationship between temperature and pressure ismaintained all the Way up to these terminal values. The choice of valuesis arbitrary, but for illustration, the point of fifteen hundred poundsper square inch pressure and 900 degrees Fahrenheit tem perature istaken as the terminal point. Likewise arbitrarily chosen is an initialpoint of 400 degrees temperature and zero pounds per square inchpressure. If a straight line B is then established between such initialpoint and the terminal point, it is found that corresponding to sixhundred pounds per square inch pressure is a temperature ofapproximately 600 degrees Fahrenheit and that each pressure has acorresponding temperature falling on the straight line. The importantfactor is that if the intermediate pressures and temperatures are alwaysrelated as represented by this line, they are always in the proper ratioto their selected terminal values.

Instead of merely responding to pressure and temperature at theirterminal values, and when it is too late to correct deviations, thepresent. control mechanism responds to the pressure and temperature allthe way from the low value of zero pounds per square inch pressure and400 degrees Fahrenheit temperature (for example) approximately along theline B until the terminal point is reached. Truly enough, in actualpractice, the relationship of pressure and temperature fluctuates eitherside of the line B as indicated by the line C but at no time does thepressure and temperature relationship achieve a value below thesaturation curve A. Under all circumstances, except possibly at the verylowest starting pressures, the product of the generator 19 issuperheated steam very close to the desired characteristics. Since thetemperature and pressure relationship is maintained at selected valuesthroughout the entire range, in actual practice the control systemdescribed herein prevents the generator from hunting widely over anenormous range as is natural to a series tube generator without acontrol system.

To accomplish this end, on the base plate 36 of the control box isprovided a proportioning switch 141 (see Figs. 2 and 4) identical withthe switches 59, 123 and 57 except that instead of being mounteddirectly upon the base plate 36, it is mounted on a slide plate 142having a central reenforcement 143. The plate 142 is slidable on thebase plate 36 because of the provision of elongated slots 144 andfastenings 146 eifective to clamp the slide plate 142 with its switch141 and pertinent mechanism in any selected position within wide limits.The switch 141 is included in an electrical circuit extending from theconductor 58 through a conductor 147 to the solenoid 17 regulating thevalve 16 at the inlet of the water pump 12. When the proportioningswitch 141 is closed, the valve 16 is also able to open and close (inthe fashion of a normal pump inlet valve) and the pump 12 can then pumpwater into the generator. When the switch 141 is open, the operation ofthe valve 16 is interfered with by the tie-energized solenoid 17 and thepump 12 is ineffective to pump water to the generator 19.

In order to open and close the proportioning switch 141, mechanism isprovided which is responsive both to pressure and temperature. Thepressure lever 126 not only is provided with a rod 127 on one side butis likewise provided with an extended rod 151 on the other side whichunderlies a lever 152. (See Figures 8 to 11, inclusive.) Also, the shaft47 has fastened on it by a pin 153 a bent lever 154 which underlies theother end 156 of the lever 152. The lever 152 therefore rests upon thetwo levers 154 and 126 and is positioned in accordance with therelationship of those two levers. To permit this, the lever 152 adjacentits center is provided with a fulcrum shaft 157 journalled in a boss 158carried on an actuating lever 159. This last lever 159 at one endcarries a pin 161 journalled in a hub 162 extending from the reinforcingplate 143 of the slider 142. A coil spring 163 urges the actuating lever159 downwardly so that the lever 152 is pressed normally against thelever 154 and the rod 151.

The direction of motion of the lever 154 under increased temperature isdownwardly or toward the base plate whereas the direction of the rod 151under increased pressure is upwardly. Consequently, if the fulcrum pin157 is substantially in alignment with the end of the rod 47 and theincrease of temperature, as reflected by the downward movement of thelever 154, is substantially in the desired proportion to the increase inpressure as reflected by the upward movement of the rod 151, the netresult is merely to rotate the lever 152 on the fulcrum pin 157 withoutin any wise disturbing the lever 159. A reverse operation of thepressure and temperature levers likewise, if in the proper proportion,produces no efiect upon the lever 159.

However, if the pressure increases much faster than its properproportion to the temperature, the rod 151 rises out of proportion tothe fall of the lever 154 and lifts the end 152 of the proportioninglever more than the end 156 thereof drops. Consequently, the fulcrum pin157 is lifted somewhat and the lever 159 is then lifted. When it islifted sufiiciently, the lever 159 engages the lever 166 of the switch141 and opens the circuit to the water pump solenoid 17 therebyinterrupting the operation of the water pump. The supply of water isthus held interrupted until such time as the continuing operation of theburner increases the temperature to a correspondingly greater amount andrestores the proper proportion between the pressure and temperature ofthe steam.

Periodically, when the temperature of the steam seems to exceed itsproper value proportionate to the pressure within the generator, thelever 154 permits the end 156 of the lever 152 to drop, lowers the lever159 and permits the lever 166 to close the switch 141 to energize thesolenoid 17 and thus makes the pump 12 effective to supply additionalwater. The additional water supply continues until the increasedpressure is out of proportion with the then existing temperature and theswitch is opened and the pump again deactivated. It is thus possible tomaintain the temperature and pressure relationship within a close rangethroughout the entire operation of the generator from low temperatureand pressure up to the maximum desired.

While the slope of the line B in Figure 12 indicates a certainrelationship of pressure and temperature, it is possible to vary theslope to some other relationship; for example, to start at say, 500degrees Fahrenheit and at zero pounds per square inch pressure and keepthe same terminal values. That is accomplished by loosening the screws146 (Fig. 2) and moving the slider plate 142 either upwardly ordownwardly so that, as shown especially in Figures 9 to 11, inclusive,the effect of the pressure and temperature levers on the proportioninglever 152 is not equal. This is especially illustrated in Figure 11 inwhich a displacement or movement in an amount indicated by the arrow 171has been accomplished over the previous setting. In this case, thetemperature lever 154 is much closer to the fulcrum 157 than is thepressure lever 151. Changes in temperature, therefore, are far moreeffective than are changes in pressure. The proportion is thereforeestablished at this new value. Equally, the displacement 171 can be inthe opposite direction and in any selected amount within the limits ofthe apparatus. By the provision of this device, a steam generator iscontrolled so that the pressure and temperature at all times are veryclose to their desired relative values.

What is claimed is:

1. A steam plant and controller comprising a steam generator, a heaterfor supplying heat to said generator, a device for supplying water tosaid generator, and a mechanism for turning said device on when thesteam temperature in said generator is over a set relationship to thesteam pressure in said generator and for turning said device ofl? whenthe steam temperature in said generator is under said set relationshipto the steam pressure in said generator.

2. A steam plant and controller comprising a steam generator, a heaterfor supplying heat to said generator, 8. pump for supplying water tosaid generator, means for turning said heater and said pump off when thesteam pressure in said generator exceeds a set value, means for turningsaid heater off when the steam temperature in said generator exceeds aset value, and means for turning said pump off when the proportion ofsteam pressure in said generator to steam temperature in said generatorexceeds a set value.

References Cited in the file of this patent UNITED STATES PATENTS1,827,950 Mulligan Oct. 20, 1931 1,961,395 Schlobohm June 5, 19341,975,086 Dickey Oct. 2, 1934 2,088,623 Thompson Aug. 3, 1937 2,342,615Newton Feb. 22, 1944 (Other references on following page) UNITED STATESPATENTS 10 V Hennessy Feb. 1, 1949 Gebhardt Nov. 1, 1949 Price Dec. 9,1952 Christiance Nov. 10, 1953 FOREIGN PATENTS France Aug. 21, 1934

